This invention relates to rock breaking apparatus of the type that break out rock fragments by the penetration of metal tools and more particularly to an apparatus capable of imparting high forces to rock cutters in order to drive them into rock and break out rock fragments while transmitting only a small portion of the impact force and rock reaction force to the bearings and shaft or other means which support the cutters. While the apparatus is primarily intended for breaking up rock, it can equally as well be used to break up similar brittle materials such as concrete or ice.
Mechanical equipment currently available for continuously or selectively breaking out rock fragments from massive rock bodies all work by driving a metal tool into the rock surface under the action of high thrust forces. The necessary thrust forces are generated at the tool and rock interface either by the application of high static loads or by impact stresses passing through the tool.
One commonly available type of rock cutting tool is a roller rock cutter used almost exclusively on hard rock tunneling machines and large hole borers, and rolled over the rock surface under essentially steady thrust loads to force the cutting edges into rock as the cutter turns. The cutting edges on the cutters are formed as a tapered disc, studs or gear-shaped teeth and, without exception, require high thrust forces to the order of 40,000 lbs per cutter to penetrate rock and spall out chips. The required thrust is generated by clamping the machine that holds the cutter against the side walls of the tunnel and then jacking between the cutters and clamping points. The cutter thrust load must be applied to the cutting elements through a massive framework and high-load-capacity bearings. Furthermore, up to 30% of the power generated by the apparatus must be expended to rotate the cutters under the high loads merely to overcome the friction between the rock and cutters and the friction in the bearings.
Because of the massive nature of conventional hard rock tunneling machines, several disadvantages exist. For example, because they are so large and heavy, there are major installation and removal problems that can seriously influence their effectiveness. This is particularly the case when access to the forward face of the tunnel is required for drilling and blasting rock that is beyond the rock cutting capabilities of the cutters or where the rock above the tunnel face requires support to prevent rock falls over the machine. Another disadvantage is that the thrust load that can be applied to the cutters on conventional hard rock tunneling machines is limited by the load bearing capacity of the cutter bearings. This limits the hardness of the rock that can be cut by such machines. Further, because the cutter bearings are generally loaded close to their capacity, a high rate of bearing failure is experienced.
Roller-type rock cutters are also widely used on shaft and raise boring machines. In this type of machine, the rotation and thrust on the boring head, onto which the cutters are mounted, is applied through rods connecting the boring head to a drive unit situated at the entrance to the raise or the shaft. The thrust force that can be applied to the cutters is limited by the strength of the drill rods. Because the rods must apply torque in addition to the thrust force, rod failure is a common occurance.
In rock machining and texturing operations that follow quarrying, it is often necessary to machine the rock to specified surface flatness or texture. Currently, this is done by sawing the rock using diamond-tipped circular saws or by abrading the rock using hard metallic powders held in contact with the rock by saws or twisted wire. Another technique that can be used with certain "spallable" rocks is to rapidly heat up the surface of the rock, causing flakes to spall off under the high thermal gradients created. Rock sawing is slow, while diamond sawing is expensive. On the other hand, thermal spalling is suitable for only a few types of rock. Roller-type rock cutters are not suitable for dressing quarried rock, mainly because of the high thrust forces required to drive the cutting edges into the rock and the resulting massive machine framework that would be required to provide and contain these thrusts.
An object of the invention is to provide a roller cutter rock cutting apparatus that can be rolled over the surface of a rock face to break out rock fragments in continuous cuts and in which only a small fraction of the thrusts needed to drive the cutting edges into the rock are applied through the roller cutter support bearings. A further object of the invention is to provide a rock cutting apparatus that does not require a massive support structure and that can be used to selectively break out rock or mineral at the working face in a mine or quarry.